Presently, photographic materials using a silver halide photographic emulsion are used for various purposes in the market, and the market scale has been increasingly expanding.
In a market for photographic materials, particularly photographic materials for color prints, characterized by a strong demand for large print volumes short delivery times, shortening development processing time is directly linked to improving production efficiency for prints. As such many studies have been made to increase developing speed.
In particular, it is well known that an increase in the silver chloride content of silver halide emulsions used in photographic materials brings about a great improvements in the developing speed.
However, it is also known that when emulsions high in silver chloride content are used, fogging is high, high sensitivity is difficult to obtain, and there is a large occurrence of so-called reciprocity failure, where sensitivity changes due to a change in exposure illuminance.
Various techniques are disclosed to overcome the above defects involved in silver halide emulsions having high silver chloride contents (hereinafter referred to as high silver-chloride emulsions).
For example, JP-A ("JP-A" means unexamined published Japanese patent application) Nos. 95736/1983, 108533/1983, 222844/1985, and 222845/1985 disclose that, in order to render high-silver-chloride emulsions highly sensitive, various grain structures, for example, those having a layer high in silver bromide content, are provided in silver halide grains. However, the inventor's study has revealed that although high sensitivity can be obtained according to these techniques, when pressure is exerted on the emulsion grains, desensitization is liable to occur, which is a great defect in practice. It has also been found that by these techniques it is difficult to adequately reduce reciprocity failure associated with high-silver-chloride emulsions.
For example, JP-A Nos. 139323/1986 and 171947/1984 or British Patent No. 2109576 A indicate that if a compound of a metal of Group VIII is contained, high sensitivity can be obtained and reciprocity failure can be lessened. JP-B ("JP-B" means examined Japanese patent publication) No. 33781/1974, JP-A Nos. 23618/1975, 18310/1977, 15952/1983, 214028/1984, and 67845/1986, German Patent Nos. 2,226,877 and 2,708,466, and U.S. Pat. No. 3,703,584 indicate that when a rhodium compound or an iridium compound is included, gradation can be made hard and reciprocity failure can be reduced. However, when a rhodium compound is used, although an emulsion whose gradation is hard can be obtained, considerable desensitization takes place, which is undesirable in practice. Further, in a high-silver-chloride emulsion containing an iridium compound, remarkable latent image intensification takes place in a relatively short period of time, (i.e., in 15 sec to about 2 hours after exposure), as disclosed by Twicky in Journal of Photoqraphic Science, Vol. 33, page 201. If such a phenomenon occurs, the development density will change conspicuously with the lapse of time from exposure of the photographic material to its processing. That is also undesirable in practice.
Further, U.S. Pat. No. 4,269,927 indicates that when cadmium, lead, copper, zinc, or a mixture of these is contained within surface latent image-type high silver-chloride emulsion grains whose silver chloride content is 80 mol % or over, high sensitivity can be obtained. However, this provides only a little effect in terms of increasing sensitivity or reducing reciprocity failure, and they have not provided emulsions of improved practical performance.
JP-B No. 35373/1973 indicates that when a water-soluble iron compound is contained in a silver chloride emulsion obtained by normal precipitation, a black and white photographic paper whose gradation is hard can be obtained inexpensively. However, in this method, if the amount of the iron compound is increased to obtain high sensitivity, desensitization is liable to take place when the emulsion undergoes pressure, resulting in a practically inadequate effect.
Further, JP-A No. 105940/1989 discloses a technique for lessening reciprocity failure by co-depositing an iridium compound to be contained in a high-silver-chloride emulsion together with silver bromide localized phases having a silver bromide content of 20 mol % without causing latent image sensitization. However, for example, this technique cannot reduce the reciprocity failure of emulsions made up of pure silver chloride, and a change, for example, in the reaction condition under which silver bromide localized phases are co-deposited will result in latent image sensitization. This technique is desired to be improved further.